Sixth Street Bridge

About this property

The Roberto Clemente Bridge, also known as the Sixth Street Bridge, spans the Allegheny River in downtown Pittsburgh, Pennsylvania, United States. The original bridge at the site was a wooden covered bridge with six spans, probably using Burr trusses. It was built in 1819 by a contractor named Lothrop. In 1859, the second Sixth Street Bridge was built by John A. Roebling. This was his third and final bridge in Pittsburgh. His eldest son Washington Roebling worked with him on the bridge after completing his degree in engineering. This bridge had two main spans of 343 feet (105 m), with shore spans of 179 feet (55 m). The floors were suspended from wire hangers, which were suspended from wire catenaries. This bridge was demolished in 1892, as it was too narrow and fragile to support modern transportation demands. In 1892, the third Sixth Street Bridge was built by engineer Theodore Cooper for the Union Bridge Company. The main spans were 440 feet (130 m) long, each having through trusses of the camel-back type with upward-angled upper chords. The spans were twice as wide as the previous bridge. In 1927 the bridge had to be taken apart because the steelwork was too brittle for safety. That year, the main spans were somewhat trimmed down temporarily from their 80-foot (24 m) height. They were lowered onto barges and floated down the Ohio River to the back channel of Neville Island, where they were used as part of the Coraopolis Bridge. Finally, in 1994 the steel was scrapped. The current bridge was completed on September 29, 1928. It is one of the Three Sisters bridges, which include the 7th and 9th Street bridges. The three bridges are nearly identical self-anchored, eye-bar suspension types. The horizontal pull of the top cords is resisted by the steel girders along each side of the roadway. The suspension system consists of 14" eye-bars extending from end to end, having two pins on the top of each tower and carrying the roadway by 4" eye-bar suspenders at the panel points. The stiffening system consists of triple web-plate girders parallel to the road grade. The girders are subjected to stresses due to bending combined with direct compression. All three bridges were fabricated and erected by American Bridge (AB). In an innovative approach, AB temporarily turned the eye-bar catenary/deck girder system into a truss by adding a diagonal to enable erection by a balanced cantilever. This avoided falsework in the river. Named for the Pittsburgh Pirates baseball player Roberto Clemente, it is one of three parallel bridges called The Three Sisters. The Three Sisters are self-anchored suspension bridges and are significant because they are the only trio of nearly identical bridges—as well as the first self-anchored suspension spans—built in the United States. Over 720 bridges link the city districts.

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Property data from the National Register of Historic Places, National Park Service (public domain).

Description adapted from Wikipedia under the Creative Commons Attribution-ShareAlike 4.0 International License.

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